Optimized heat roll apparatus

ABSTRACT

One embodiment of the heated roll apparatus uses an optimized roll whose surface layer is composed of a material responsive to being heated, particularly by external magnetic induction, and the depth of which, as well as the construction of the rest of the roll, uses one or more other materials whose properties are optimized with respect to maximizing the roll&#39;s rate of temperature change, minimizing energy usage, and performing the intended application. A thin outer ferrous layer over top of a thicker ceramic, insulating layer may be used. The roll may also include an outer layer that is responsive to heating, particularly by magnetic induction, and one or more inner layers of different material(s) chosen to increase the roll&#39;s rate of temperature change and reduce energy usage, but which are further selected to promote rapid lateral heat conduction to reduce lateral temperature variations. This roll could include a thin outer ferrous layer over top of a thicker aluminum core. The roll may instead be constructed of a single contiguous material (such as a carbon-fiber composite) that is particularly responsive to heating by magnetic induction, and which has a higher strength-to-weight ratio than ferrous alloys (i.e. cast iron or steel), thereby allowing it to be lower in weight and more thermally responsive than conventional heated rolls. The roll may also have a surface layer or contiguous depth composed of a material responsive to being heated, particularly by magnetic induction, but which in addition has a minimal outside diameter (regardless of its internal construction) in order to minimize its mass, so that it can be heated more quickly to a higher temperature, by a given heat input rate generated by any means, than would be possible with a larger, conventional heated roll.

FIELD OF THE INVENTION

This invention relates to heated rolls used in web processing operationssuch as: calendering; drying; laminating; embossing; pre-heating;corrugating; curing; heat-setting, shrinking; bonding; etc. It hasparticular application to roll surface materials responsive to hightemperature induction heating, where energy losses associated withconventional, indirect heating systems can be significantly reduced.

BACKGROUND OF THE INVENTION

The surface layer of most heated rolls is typically thick-walled andmade of a ferrous alloy, while other more specialized, usually unheatedrolls use other metals (e.g. aluminum) as well as non-metal materialssuch as granite. Heated rolls are typically heated internally, using hotwater, hot oil, or steam, and may also be heated externally using steamjets, gas flames, hot air impingement, infra-red radiation, or magneticinduction. The depth of the surface layer of conventional heated rollsis typically greater than is necessary for the application at hand.While this may be due to strength considerations, it is often due to alack of appreciation of the how this depth affects the process responsetime, energy consumption, and required heating system size. The appliedheat may also be free to migrate in the cross-direction through theroll's thick outer wall at a rate higher than is optimal for thespecific application. Or, conversely, the relatively low thermalconductivity of ferrous metals may limit the lateral heat conduction toa rate lower than is optimal for a specific application. The followingare examples of these various situations;

Web Calendering Applications

In some continuous sheet producing industries (such as papermaking andmetal sheet or foil manufacturing), in one of the final steps, commonlyreferred to as calendering, the web is passed between heavy, stiff rollsthat are loaded against one another to compress the web and make it moredimensionally uniform. Calendering rolls are typically thick-walled andmade of a ferrous alloy and are most commonly heated by a hot internalfluid flow, using hot water, hot oil or steam. The historical use ofinternal heating fluids, and the need for high roll stiffness duringcalendering has resulted in conventional heated calendering rolls beingrelatively thick-walled (typically with wall thickness of more than oneinch, or solid throughout), with elaborate and expensive cross-boredfluid channels and rotating seals. Furthermore, conventional heatedcalendering rolls are made of an essentially homogeneous, moderatelythermally-conductive material, such as steel, throughout their full wallthickness, to permit unimpeded heat conduction from the inside to theoutside. The external fluid heating systems that accompany conventionalheated calendering rolls are also relatively inefficient due to pipingcircuit heat losses and energy conversions losses (their original sourceof energy is often natural gas or heating oil, requiring energyconversion with attendant combustion and heat exchanger inefficiencies).Requisite external fluid temperature control systems must also be ableto cool the fluid (to enable precise roll temperature control, and toremove the heat quickly during stoppages), which adds to the overallcomplexity and cost.

A primary limitation of conventional heated calendering rolls is thatthey are relatively thermally-conductive throughout their substantialdepth, requiring that their whole mass be heated up to attain a desiredouter surface temperature. Furthermore, the large mass of internal fluidused by conventional heated calendering rolls also has to be heatedbefore it can heat the roll, or cooled before it can cool the roll. Thelarge roll and fluid mass, and the long radial conductive paththroughout the depth of the roll, thus produces a large thermal inertiathat reduces the response time of roll temperature controls to processdisturbances on continuous operations, and which furthermore thusimposes a severe setup and change-over delay on discontinuous,batch-type calendering processes. A further consequence of this largethermal inertia is that external fluid cooling and heating systems mustbe significantly over-sized to cool and heat the rolls fast enoughbefore and after stoppages. Over-sizing these fluid-cooling and heatingsystems beyond what steady-state conditions require adds significantlyto their size, complexity and initial cost, and further aggravates theirinherent energy inefficiencies. A further limitation of conventionalheated calendering rolls is that they are homogenous across their width,and the internal fluid paths are continuous across their entire width,making it impossible to locally heat just one cross-direction region ofthe roll. Even if a localized external heating means, such as magneticinduction or forced-convection heating using hot air impingement, isused to heat just one cross-direction region of the roll, the appliedheat will conduct laterally through the roll, diminishing the localizedeffect.

Web Drying Applications

While there are many types of webs that are dried using heated rolls orheated metal cylinders, a typical one is a wet paper web, where in thecase of paper manufacturing, it is upstream of the calendering processdescribed above, and the web is typically first dried by passing itaround steam-heated metal cylinders that are typically referred to asdryer cans. To permit heat conduction from the inside to the outside,dryer cans are usually made of a ferrous material such as cast iron, andare usually relatively thick-walled to support their own weight and thatof the internal condensate, and to withstand the internal steampressure.

The response time and cross-direction heat migration limitationsmentioned above for web calendering applications apply equally to webdrying applications.

Web Converting Applications

In certain web converting processes, such as web embossing, weblaminating, or paper corrugating, a common manufacturing step is to passindividual web layers around one or more heated, ferrous, relativelythick-walled preheating cans or rolls to dry and pre-heat the layersbefore they are embossed or laminated together. The two or more rollsthat form the embossing or laminating nips through which the web passesare also typically heated.

In embossing applications the purpose may be to thermally soften the webto make it more malleable. On laminating applications the purpose may beto preheat and dry the individual layers after rewetting or coating toreduce or prevent curl of the final laminated product, or to simply addheat to the process to facilitate intra-layer bonding during laminating.On all laminating and embossing applications it is generally desirableto ensure a very uniform (i.e. +/−1% of process) roll surfacetemperature profile across the width of the process. If the rolltemperature is not sufficiently uniform it may impart a non-uniformtemperature profile to the web(s) before or during laminating orembossing. This in turn may affect the web's localized compressibility,malleability, and dimensional stability, leading to variable finishedproduct quality. While on high throughput web manufacturing operationssuch as papermaking it is cost effective to measure and control webproperties in narrow zones across the width, such investments areusually not viable on converting applications that are typically muchnarrower and slower. Consequently, narrow zone control of effective rollheating means such as external magnetic induction, is often notcommercially viable on converting applications. The common solution isthen to use enhanced internal heat conduction means, such as helicalfluid channels or phase change heat pipes, to promote lateral heatconduction and minimize lateral temperature variations. Unfortunately,such rolls are relatively expensive to build, they often require fluidconnections, and they typically require a significant internalstructural mass, which along with the internal fluid itself, adds totheir thermal inertia to lengthen their heat-up response.

In paper corrugating applications the purpose is typically to heat anddry the individual paper layers in a controlled manner before gluingthem together. Controlled drying of the outer paper layers duringcorrugating prevents or reduces warp of the combined final product,while controlled heating of both the inner and outer paper layerssupplies the precise amount of process heat to gel, but not prematurelycrystallize, the starch-based adhesive.

The response time and cross-direction heat migration limitationsmentioned above for web calendering applications apply equally to webconverting applications, especially in that preheating cans arehomogenous across their width, with a single internal steam chamber,making it difficult to locally heat just one lateral region of thepreheater can to localize the drying or heating effect in a givenlateral region of the web.

Web Curing and Heat-Setting Applications

In certain other web producing and handling industries, many of whichare discontinuous, batch-type processes (such as for bonded nylon fabricproduction for mesh or textile manufacturing), a common manufacturingstep is to pass the web around one or more internally-heated metal rollsto dry and cure the material, to achieve a final target moisture, setand cure adhesive bonds, and shrink the web to its final, stabledimensions.

As with the previously described heated calendering applications, thehistorical use of internal fluids has resulted in conventionalcuring/heat-setting rolls being relatively heavy-walled with elaborateand costly internal fluid channels and rotating seals. Thesecuring/heat-setting rolls are also made of a homogeneous,thermally-conductive material, such as steel, throughout their depth,and are also typically accompanied by an expensive and over-sizedexternal fluid cooling and heating system to quickly remove and add heatbefore and after stoppages. Curing/heat-setting rolls are alsohomogenous across their width, and the internal fluid paths arecontinuous across their entire width, making it impossible to locallyheat just one cross-direction region of the roll. This has a unique,negative implication on curing/heat-setting applications. Web shrinkageis typically a somewhat non-uniform phenomenon, occurring more freelyand uniformly at the edges, and less easily and uniformly near thecenter of the web due to friction between it and contacting machineelements, such as rolls. This cross-direction non-uniformity oftenproduces wrinkles in the web as it shrinks, which in turn may have adeleterious effect on the final quality of the web. If thecuring/heat-setting roll could be heated in the center first, and thenthe heating application gradually broadened out toward the edges at anoptimum, controlled rate, web wrinkling problems could perhaps bereduced or eliminated.

The above examples clearly illustrate that on many web manufacturing andconverting applications the design of conventional heated rolls, andtheir method of heating, imposes significant limitations, and that theselimitations will apply equally or in part to other web applicationsinvolving heated rolls.

Induction Heating

As mentioned above, and as disclosed in U.S. Pat. No. 4,384,514, ferrousmetal rolls used on web manufacturing and converting applications can beexternally heated by magnetic induction, whether or not the roll is alsosimultaneously heated by an internal heated fluid flow. Recentadvancements in induction heating technology permit very reliableoperation at high power densities (>50 kW power transmission/meter ofroll width), to enable very reliable and efficient, rapid externalheating of the surfaces of ferrous metal rolls to much highertemperatures than was previously attainable. Unfortunately theabove-described conventional rolls cannot fully exploit the benefits ofthis new induction heating technology.

The heavy mass of conventional steel rolls or cans, the heat capacity oftheir thick steel walls, and the volume and heat capacity of internalcooling and heating fluid, all add to the substantial thermal inertia ofthese systems. Even though state-of-the-art induction technology heatsjust the surface region of a steel roll, where the thermal energy isactually needed by the process, that heat must unfortunately migrateinto the roll and internal fluid, and heat up the entire combined massbefore the surface temperature can be stabilized at a target value.

It is therefore an object of the present invention to provide a newapparatus using any one of a family of rolls, all consisting of arelatively thin outer layer that can be rapidly heated by any of thevarious external heating modes mentioned above, and a supportive corestructure that will not easily absorb or conduct heat, that isfabricated of lighter-weight material with a much lower specific heatand thermal conductivity.

Another object of the present invention is to provide heated rolls inwhich the supportive core structure is fabricated of a material with arelatively high thermal conductivity, such as aluminum.

Still another object of the present invention is to provide heated rollsfabricated of a single contiguous material that is both responsive toeternal magnetic heating and also relatively lightweight.

A still further object of the present invention is to provide heatedrolls that are of minimal diameter so that its surface and end wall heatlosses are minimized, thereby allowing it to be heated to a highertemperature.

Another object of the present invention is to provide heated rolls thathave a relatively lower thermal inertia than conventional rollspresently used for the same purposes, so that substantially less powerwill be needed to heat their surfaces to a given temperature in a giventime period, and then maintain it there.

Yet another object of the present invention is to provide rolls withminimal thermal mass to facilitate more rapid cooling (which will beparticularly advantageous on discontinuous, batch-type processes) bysimple means, such as an external, inexpensive, forced-air convectioncooling plenum, thereby eliminating the need for complex and expensiveinternal fluid cooling systems.

A further object of the present invention is to provide composite rollsthat can be segmented in the cross-direction dimension to allow adjacentexternal heating elements to selectively heat given regions of the roll.

SUMMARY OF THE INVENTION

A web processing apparatus of the present invention includes (A) a rollconsisting of (i) a composite annular structure, having a thin outershell or sleeve, typically less than a ¼ inch thick, made of a firstmaterial capable of being heated to the desired temperature by a knownexternal heating method, and an inner, typically thicker sleeve or core,made of a second material that is highly non-conductive in bothelectrical and thermal respects and able to withstand said desiredtemperature; said composite annular structure being suitably constructedand reinforced so that the exterior surface of the outer sleeve isexposed, and the outer sleeve and inner sleeve or core are adequatelyanchored to one another, enabling the composite annular structure toperform the desired function effectively and reliably; and (ii) a finalsuitable structure supporting said composite annular structure to permitmounting and rotation of the roll; (B) a device for externally heatingthe outer sleeve of the composite roll.

In another embodiment of the present invention the inner sleeve or coreof the web processing apparatus is made of a second material that ishighly thermally conductive and able to withstand said desiredtemperature. The web processing apparatus could also include (A) anoptimized roll manufactured from a contiguous material such ascarbon-fiber composite, which thereby has a significantly lower thermalmass, higher strength-to-weight ratio, and higher surface emissivitythan conventional rolls manufactured from ferrous alloys, and (B) adevice for externally or internally heating such optimized roll.

In another embodiment of the present invention, the web processingapparatus includes (A) an optimized roll manufactured from a materialresponsive to heating by external magnetic induction (such as steel orcarbon-fiber composite), that has a minimal outside diameter (typically<12″ diameter) in order to minimize its thermal mass, so that it can beheated by a given induction-generated heat input (typically >20 kW/meterroll width) to a higher temperature (typically >>150° C.) than would bepossible with a larger, conventional heated roll, and (B) an externalmagnetic induction heating device with a power output (typically >20kW/meter roll width) that is sufficient to heat the roll of the presentinvention to a relatively high temperature (typically >>150° C.).

The optimized heated roll apparatus of the present invention may bebeneficially applied and heated by any external (i.e. steam jets, gasflames, hot air impingement, and infra-red radiation) or internal method(i.e. internal magnetic induction, or hot fluids such as hot water, hotoil or steam). However, the various embodiments described herein of thepresent invention are particularly suited to heating by externalmagnetic induction, which is typically simpler to apply and/or moreenergy efficient than other potential heating methods.

The optimized heated roll apparatus of the present invention isgenerally designed to enable faster, more controllable heating, to ahigher temperature, with lower energy expenditure, and cooled morequickly with a simpler cooling system, than conventional rolls that arepredominantly manufactured from ferrous alloys. The preferredembodiments of the present invention therefore each provide somecombination of the following core advantages;

-   -   Lower thermal mass (mass×specific heat) than conventional heated        ferrous rolls, enabling faster heating by external induction and        faster cooling by any suitable means.    -   More conductive interior material properties than conventional        heated ferrous rolls, enabling higher lateral heat conduction to        reduce lateral temperature variations.    -   Smaller diameter than conventional heated ferrous rolls,        enabling heating by external induction to higher temperatures    -   Higher surface emissivity than conventional heated ferrous        rolls, allowing the roll's surface temperature to be measured by        non-contact Infrared means.

Specific applications where the various embodiments of the presentinvention would apply include numerous continuous and batch-type webmanufacturing processes, such as:

-   -   web calendering applications, such as during papermaking,        plastic film and sheet manufacturing, and metal sheet or foil        manufacturing.    -   web primary and secondary drying applications, such as during        paper, fabric or film manufacturing.    -   web converting applications, such as during paper labeling,        laminating, or printing.    -   corrugated board curing and drying applications, such as during        constituent paper preheating or combined board curing and        drying.    -   web curing and heat-setting applications, such as during layered        and/or bonded fabric production for mesh or textile        manufacturing.

While the embodiments of the present invention apply particularly wellto the applications listed above, they will apply equally or in part toother web manufacturing applications involving heated rolls.

BRIEF DESCRIPTION OF THE DRAWINGS

Having thus generally described the nature of the invention, referencewill now be made to the accompanying drawings that schematicallyillustrate embodiments thereof.

FIG. 1 is a length-wise sectional-view of a preferred embodiment of thepresent invention in which an optional adjacent forced-convection airplenum is also shown.

FIG. 2 is a length-wise sectional-view of an alternate arrangement ofthe embodiment of FIG. 1 where the outer shell is divided into separateouter annular sections to reduce lateral heat conduction from onesection to the next, and where an optional, adjacent, magnetic inductionheating systems is shown consisting of individual inductors of limitedwidth.

FIG. 3 is a length-wise view of an alternate arrangement of theembodiment of FIG. 1, where the outer shell's annular sections areinclined so that no position across the web is ever exposed to acontinuous, potentially cool seam between adjacent annular sections.

FIG. 4 is a sectional-view of a length-wise portion of the preferredembodiment of FIG. 1, where the substantial space between a thin outershell and inner supporting core is filled with an expandable,high-temperature, structural foam to form a composite roll.

FIG. 5 a is a sectional-view of a length-wise portion of the embodimentof FIG. 1 where the roll is constructed of individual disks, eachcomposing a thin annular outer shell, an inner annular core, andintervening, high-temperature, structural foam.

FIG. 5 b is an elevational view of the embodiment shown in FIG. 5 a.

FIG. 6 is a sectional-view of an angular segment of a conventional rollused for curing/heat-setting applications.

FIG. 7 is a graph illustrating the typical time-wise response achievablewith induction heating on a conventional curing/heat-setting roll of thetype shown in FIG. 6.

FIG. 8 is a graph illustrating the relative improvement in time-wiseresponse that would be achievable with induction heating on compositerolls of the types shown in FIGS. 4, 5 a and 5 b.

FIG. 9 a is a cross-sectional view of a preferred arrangement of analternate embodiment of the present invention, showing an optimized rolland an adjacent magnetic induction heating device, wherein the roll ismanufactured from a relatively thin outer layer consisting of a materialthat is particularly responsive to external induction, such as steel orcarbon-fiber composite, and a relatively thick inner layer of a materialthat is less dense and that has a relatively high thermal conductivity.

FIG. 9 b is a sectional plan-view of the embodiment shown in FIG. 9 b.

FIG. 10 a is a graph illustrating the steady-state surface temperatureproduced by a variable heat input profile, derived using a finiteelement analysis of a composite roll consisting of a thin outer ferrouslayer and a thicker inner aluminum layer, of the type shown in FIGS. 9 aand 9 b.

FIG. 10 b is a graph illustrating the steady-state surface temperatureproduced by the same variable heat input profile, derived using the samefinite element analysis, of a steel roll with the same outside andinside diameter as the composite roll analyzed in FIG. 10 a.

FIG. 10 c is a graph illustrating the steady-state surface temperatureproduced by the same variable heat input profile, derived using the samefinite element analysis, of a steel roll with the same outside diameterand weight as the composite roll analyzed in FIG. 10 a.

FIG. 11 a is a cross-sectional view of a another embodiment of thepresent invention, showing an optimized roll manufactured of a suitablecontiguous material such as carbon-fiber composite, a web in contactwith said roll, and a suitable, adjacent external heating device such asa sectionalized magnetic induction actuator.

FIG. 11 b is a plan-view of the arrangement shown in FIG. 1 a, showingin addition an adjacent, optional, forced-convection cooling air plenum.

FIG. 12 is a cross-sectional view of an alternate arrangement of theembodiment show in FIG. 1 a, showing an optimized roll manufactured of asuitable contiguous material such as carbon-fiber composite, withinternal fluid-carrying channels that may be used to replace orsupplement other roll heating and/or cooling means.

FIG. 13 a is a cross-sectional view of embodiment of the presentinvention, showing an optimized, small diameter roll manufactured from asuitable material such as steel or carbon-fiber composite, a web incontact with said roll, and an adjacent magnetic induction heatingdevice.

FIG. 13 b is a plan-view of the embodiment shown in FIG. 13 a.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIG. 1, a preferred embodiment of the rolls 100 of thepresent invention is shown. While there are numerous ways in whichsuitable composite rolls 100 can be constructed by those skilled in theart of manufacturing rolls to meet the needs of specific applications,the arrangement illustrated in FIG. 1 is just one example involving thepresent invention.

Referring again to FIG. 1 the composite roll consists of a thin ferrousouter shell 1 (approximately 3/16 inch thick) surrounding a thicker(approximately 4 inch thick) non-metallic sleeve 2 made from apreferably cast, suitable material, such as cement, that is adequatelynon-conductive in both electrical and thermal respects. The materialmaking up the sleeve 2 should have a thermal mass that is one half orless than the thermal mass of steel. The cement (or equivalent) may havereinforcing bars 3 within it, and/or the outer shell 1 may have metallicprotrusions 4 or hooks that will anchor it within the cement to addstrength to the composite annular structure. If the cement used hasapproximately the same coefficient of expansion as the outer shell 1,the outer shell 1 might be partially embedded in the thicker innersleeve 2. Metallic end caps 5 might also be anchored into the innersleeve 2, by means of fasteners 6. Shaft extensions 7 might then bewelded on to the end caps 5 to permit mounting and rotation of the roll.The ends of the outer shell 1 should also be heat-insulated to avoiddirect thermal contact with the metallic end caps 5. When very highsurface temperatures are used the thermal expansion coefficient of thematerials used in the outer shell 1 and inner sleeve 2 should be closelymatched.

As mentioned above, those skilled in the art of manufacturing rollscould provide other ways to achieve the desired, annular, composite rollstructure, and to design and manufacture an additional supportivestructure to permit mounting and rotation of the roll.

Referring still to FIG. 1, an adjacent forced-convection air plenum 8can also be added to provide inexpensive, external, non-contact coolingof the roll's outer shell 1 to facilitate a rapid response time and/orto act in combination with whatever external heating system is used toheat the roll (e.g. steam jets, gas flames, hot air impingement, ormagnetic induction). In addition, when a preferred means of externalheating is used, such as magnetic induction, the outer shell 1 would bemanufactured from a ferrous alloy that is particularly responsive tomagnetic induction.

Referring now to FIG. 2, the arrangement shown in FIG. 1 can be furtherenhanced by dividing the outer shell into separate annular sections 9 toreduce lateral heat conduction from one section to the next. Suchannular sections 9 could be further thermally isolated from one anotherby narrower, intervening, ring-shaped insulating strips (not shown).Commercially available inductive roll heating systems typically consistof individual inductors of limited width, typically between 60 and 120mm wide. Inductors of suitable design and specification are disclosed inU.S. Pat. No. 7,022,951 issued Apr. 4, 2006. The widths of the annularsections 9 shown in FIG. 2 could then be made to match those of theadjacent inductors 10, and be lined up with them, so that individualinductor control could be used to profile the temperature of the heatedroll as needed across its width.

As in the case of the previous arrangement shown in FIG. 1, an externalforced-air convection plenum could be added to the arrangement shown inFIG. 2, and also to all the arrangements described below, to quickly andinexpensively cool the roll's outer layer during stoppages, or wheneverthe external heating system generates a roll surface temperature thatexceeds the desired target value.

The ability to localize the external heating effect, whether the heat isgenerated by induction or other means, could be quite beneficial onpaper drying applications, to facilitate cross-directional profiling ofthe paper's moisture content. This ability could also be quitebeneficial on laminating and corrugating applications, to facilitatecross-directional profiling of the moisture and temperature of theincoming paper layers, so as to maximize the flatness, bond strength anddimensional stability of the final combined laminate or board.Furthermore, this ability could be extremely beneficial on some webcuring/heat-setting applications where it may be preferable to startheating in the center of the machine and progress outwards at acontrolled rate, to shrink the web symmetrically, and from the centeroutward, to minimize or eliminate the formation of wrinkles.

Referring now to FIG. 3, the arrangements shown previously in FIGS. 1and 2 can be further enhanced by inclining the outer shell's annularsections 11 so that no position across the web is ever exposed to acontinuous, potentially cool, continuous seam 12 between adjacentannular sections 11.

Referring now to FIG. 4, an alternative embodiment of the presentinvention is shown that includes a relatively thin outer shell 13, aninner solid or annular core 14, and an intervening annular space filledwith a specialized insulating material 15 chosen for its sufficientsolidity, low density, and low thermal conductivity. A suitableinsulating material 15 might be an expandable, high-temperature,structural foam, such as TEPIC™, that has been recently developed by theUS Department of Energy's Sandia National Laboratories in Livermore,Calif. To facilitate external magnetic heating of the composite rollshown in FIG. 4, and to ensure adequate structural stiffness, the outershell 13 would be manufactured from a ferrous alloy, and the inner core14 from a sufficiently strong material, perhaps of the same ferrousalloy. In addition, the inner core 14 may be annular in shape, as shown,allowing it to act as a sleeve about a full-width axle 16 (not shown incross-section). Alternatively, external pivots could be welded orotherwise fastened to the ends of a solid inner sleeve (not shown), in amanner analogous to that shown in FIG. 1, to facilitate rotation of thecomposite roll.

Referring now to FIGS. 5 a and 5 b, the arrangement previously shown inFIG. 4 can be further enhanced by segmenting the composite roll intoindividual, composite disks 17, that are each fabricated by placingouter 18 and inner 19 annular sleeves between two side plates 20 (thatare only used during fabrication), then filling the resultingcontiguous, annular cavity 21 with expandable, high-temperature,structural foam 22, then removing the temporary side plates 20. Theresulting composite disks 17 can then be slid upon a common axle 23.Furthermore, the outer 18 and/or inner 19 annular sleeves could also benotched to interlock adjacent disks 17, then end caps 24 (only one endshown, in FIG. 5 a) could be used to compress the disks 17 together toensure adequate roll stiffness.

As described above with respect to other arrangements, the individualdisks 17 could also be lined up with segmented, external heating means,such as individual inductors, to facilitate zonal temperature control,and/or inclined to prevent exposure of the web to continuous “cold”seams between adjacent disks 17.

One could also modify the foregoing arrangements to make effective andresponsive use of internal heating, by locating fluid-carrying chambersor channels between a first, relatively thin, thermally-conductive outersleeve, and a thicker, thermally-insulating layer below it. To ensureheat transfers easily, and essentially solely, to the outer sleeve, thefluid-carrying chambers or channels could be in direct thermal contactwith the underside of the outer sleeve, while being otherwise surroundedand embedded within the inner, thermally-insulating layer below, priorto connecting at the end of the roll to an external source of steam, hotwater, or hot oil.

Referring now to FIGS. 6, 7 and 8, the probable value of the variousembodiments of the roll 102 of the present invention, in terms ofheating system size reductions, response time improvements, and energysavings, may be investigated and approximated by constructing andsolving realistic, transient heat transfer models for representativeconventional and proposed roll arrangements. Referring specifically nowto FIG. 6, a typical curing/heat-setting roll 102 used in thefabrication of layered nylon fabrics (that are subsequently used inpaper manufacturing to support the paper web during pressing anddrying), would be fabricated of carbon steel and have an outer diameter25 of about 48 inches. A typical such roll would be about 12 meters wideand would consist of outer 26 and inner 27 shells (each typically about½ inch thick) joined together by intermittent spacer strips 28 (withtypical ½ inch×½ inch cross-sections) to form intervening fluid channels29 through which would flow the aforementioned roll heating and coolingfluids.

A finite difference model that assumes the conventional roll dimensionsnoted above, and accounts for induction heat input, convection andradiation losses to ambient from the surface of the roll 100, andcontact conduction losses to the fabric being cured/heat-set, and whichalso assumes the fluid channels are empty and filled with air, producesthe results plotted in FIG. 7. The initial high induction heating rate30 raises the 12 meter wide roll's outer surface temperature 31 rapidlyto the target value 32, then conducts deeper into the roll to eventuallyalso raise the temperatures of the inner surface of the roll 33 and theintervening air void 34 (in the empty fluid channels). Once the targetsurface temperature 32 is reached, the induction power output 30 can bereduced to a level sufficient to maintain the roll surface temperature31 at the target value 32 for the remainder of the production run. Toaccomplish this the model estimates an energy transfer 35 of about 147kW-hours is needed to heat the roll to the target temperature 32, thenabout 60 kW-hours/hour is needed to keep it there. A typical productionrun consisting of a 20 minute heat-up period followed by a 3-hourcuring/heat-setting period, would then consume about 325 kW-hours ofenergy (assuming 100% efficiency). Once the induction heat source isturned off, the hot roll would then cool down at a relatively slow ratedue to the absence of an internal heating/cooling fluid flow, asindicated by the overlaid temperature trajectories 36.

The same finite difference model, when applied to either of thearrangements shown in FIGS. 4, 5 a and 5 b, then produces the resultsplotted in FIG. 8. Noticeably, only about 37 kW-hours of energy 37 isneeded to raise the roll's surface temperature 38 to the same targetlevel 39 in the same 20 minute time span, and then only about 56 kW isneeded to keep it there. In addition, because the temperature 40 of theinner depths of the roll rises insignificantly, and because the thermalinertia of the roll is so much lower, external forced convection coolingusing air impingement is expected to reduce the outer surfacetemperature 38 to its original value within a mere 20 minutes, asreflected by the convection cooling airflow's rapidly decreasing spentair temperature 41. The reduced energy demand 37 during the heat-upperiod thus allows the maximum power output 42 of the induction systemto be decreased by about 75% (from about 37 kW down to 9 kW). As aresult, the induction system's design capacity can be decreased from 50kW/meter to about 10 kW/meter, to greatly reduce its size, complexityand initial cost. The ability to rapidly cool the roll with justinexpensive external air impingement would also provide the desiredcool-down response without the need for expensive and complex internalfluid systems.

Referring to FIG. 9 a, a second preferred embodiment of the roll of thepresent invention is shown. The key difference from the roll 100 of theembodiment shown in FIG. 1 is that the inner layer of the roll 104 ofthe embodiment shown in FIG. 9 a is that the inner layer of the roll 104shown in FIG. 9 a is constructed of a material selected for itsrelatively high thermal conductivity. As shown in FIG. 9 a the roll 104includes a thin ferrous outer shell 43 (approximately 1/16 inch thick orless) surrounding a thicker (approximately ¼ inch thick or more) sleeve44 made from a material that has relatively high thermal conductivityand strength-to-weight ratio, such as aluminum.

The outer, typically ferrous layer 43 can be formed by suitable meanssuch as either spray or plasma coating of steel 43 onto the underlying,typically aluminum substrate 44, or by shrink-fitting a thin, typicallysteel tube 43 around a heavier-walled, typically aluminum core 44.

The roll's outer ferrous layer is typically heated by an externalmagnetic induction heating device 45. Said magnetic induction heatingdevice 45 may be sectionalized, as shown in FIG. 9 b, to facilitatelocalized control of the roll's surface temperature across all or partof its width, thereby permitting active compensation for excessivenon-uniformities resulting from factors such as an incoming web 46 witha extremely non-uniform input temperature profile. (Commerciallyavailable inductive roll heating systems typically consist of individualinductors 47 of limited width, typically between 60 and 120 mm wide.Inductors of suitable design and specification are disclosed in U.S.Pat. No. 7,022,951 issued Apr. 4, 2006.)

Referring now to FIGS. 10 a, 10 b and 10 c, the probable unique value ofthe embodiment shown in FIGS. 9 a and 9 b, in terms of improved lateraltemperature uniformity, may be investigated and approximated byconstructing and solving a representative finite difference model forthree relevant alternative roll arrangements, as follows:

Arrangement “X”: An 8 inch outside diameter static roll, with surfaceemissivity 0.3, in a surrounding 70° F. environment, comprising a 0.020inch thick steel outer surface layer and a 0.313 inch thick inneraluminum layer, and weighing 35 lbs/meter, heated to 300° F. by anaverage heat input rate of 3.6 kW/meter, that varies across the width by+/−5%.

Arrangement “Y”: The scenario of Arrangement “X”, but where the rollcomprises a 0.020 inch thick steel outer surface layer and a 0.313 inchthick inner steel layer, and weighs 90 lbs/meter.

Arrangement “Z”: The scenario of Arrangement “X”, but where the rollcomprises a 0.020 inch thick steel outer surface layer and a 0.106 inchthick inner steel layer, and weighs 35 lbs/meter.

Referring again to FIG. 10 a, the input power 48 to the roll (heat inputper unit time) can be varied with lateral position 49 to produce asteady-state surface temperature profile 50. Referring now to FIG. 10 b,changing only the inner layer's material to steel significantlyincreases the variability of the steady-state surface temperatureprofile 51. Referring next to FIG. 10 c, reducing only the inner steellayer's thickness to produce a roll weight equal to that of thecomposite roll assessed in FIG. 10 a, further increases the variabilityof the steady-state surface temperature profile 52. This simple analysisvalidates that a composite roll consisting of an outer ferrous shell andan inner, thicker layer including a lighter, more thermally-conductivematerial, will result in a lighter roll that will exhibit a more uniformsurface temperature profile in response to a non-uniform surface heatexchange.

Referring to FIGS. 11 a, 11 b and 12, other embodiments of the roll ofthe present invention are shown. While there are numerous ways in whichsuitable optimized rolls can be constructed by those skilled in the artof advanced material science and/or manufacturing rolls, thearrangements illustrated in FIGS. 11 a, 11 b and 12, are just examplesinvolving the present invention.

Referring now to FIG. 11 a, the optimized roll 53 consists of acontiguous layer of a suitable material 54, such as carbon-fibercomposite, having a lower thermal mass (herein defined as the mass ofthe roll multiplied by the effective average heat capacity of thematerial from which it is manufactured), and strength-to-weight ratiothan a conventional roll manufactured from one or more ferrous alloys.The lower thermal mass should be one half or less than the thermal massof steel. The roll 53 may be solid throughout its depth, or hollow, asshown in FIG. 11 a.

Referring still to FIG. 11 a, the external surface 55 of the roll 53might, if needed, be finished or coated to produce a surface emissivityhigh enough to permit non-contact temperature measurement of the roll'ssurface 55. The external surface 55 of the roll 53 might also bepolished to produce a surface 55 smooth enough to prevent abrasion ormarking of the contacting web 56, and/or to facilitate a higher heattransfer rate between the surface 55 of the roll 53 and the contactingweb 56.

Referring now to both FIGS. 11 a and 11 b, roll heating may beaccomplished using a suitable means such as external magnetic induction,and said magnetic induction heating device 57 may be sectionalized, asshown in FIG. 11 b, to facilitate localized control of the roll'ssurface temperature across all or part of the roll's width.(Commercially available inductive roll heating systems typically consistof individual inductors 58 of limited width, typically between 60 and120 mm wide. Inductors of suitable design and specification aredisclosed in U.S. Pat. No. 7,022,951 issued Apr. 4, 2006.) An optionalroll cooling device, such as an external forced-air cooling plenum 59,may also be incorporated, as shown in FIG. 11 b.

The ability to localize the external heating effect, whether the heat isgenerated by induction or other means, could be quite beneficial onpaper drying applications, to facilitate cross-directional profiling ofthe paper's moisture content. This ability could also be quitebeneficial on laminating and corrugating applications, to facilitatecross-directional profiling of the moisture and temperature of theincoming paper layers, so as to maximize the flatness, bond strength anddimensional stability of the final combined laminate or board.Furthermore, this ability could be extremely beneficial on some webcuring/heat-setting applications where it may be preferable to startheating in the center of the machine and progress outwards at acontrolled rate, to shrink the web symmetrically, and from the centeroutward, to minimize or eliminate the formation of wrinkles.

Referring now to FIG. 12, one could also modify the optimized roll 53 ofthe present invention to make effective use of internal heating and/orcooling, by locating fluid-carrying chambers or channels 60 within thedepth of the contiguous material 54, and connecting said channels 60 toa suitable heating and/or cooling fluid source, such as steam, water, oroil.

Referring now to FIG. 13 a, an optimized roll 61 is manufactured from amaterial 62 that is responsive to heating by magnetic induction, such assteel or carbon-fiber composite, and has a relatively small diameter(typically <12″ diameter), and thus a lower thermal mass (herein definedas the mass of the roll multiplied by the effective average heatcapacity of the material from which it is manufactured) and smallersurface area from which to lose heat to the environment and contactingweb 63, than would a larger, conventional heated roll. The lower thermalmass should be one half or less than the thermal mass of steel. The roll61 may be solid throughout its depth, or hollow, as shown in FIG. 13 a.

Referring now to both FIGS. 13 a and 13 b, high heat flux (typically >20kW/meter roll width) roll heating is accomplished using an externalmagnetic induction heating device 64, and said magnetic inductionheating device 64 may be sectionalized, as shown in FIG. 13 b, tofacilitate localized control of the roll's surface temperature acrossall or part of the roll's width. (Commercially available inductive rollheating systems typically consist of individual inductors 65 of limitedwidth, typically between 60 and 120 mm wide. Inductors of suitabledesign and specification are disclosed in U.S. Pat. No. 7,022,951 issuedApr. 4, 2006.) The ability to localize the external heating effect usinga sectionalized induction heating device could be quite beneficial onpaper calendering and finishing applications to facilitatecross-directional profiling of the paper's caliper and/or gloss andsmoothness.

Although suitable materials from which to manufacture the various layersof the embodiments of the present invention would be steel, ceramic,carbon-fiber composite, and aluminum, those skilled in the arts ofadvanced material science and/or roll manufacturing may identify othersuitable materials that will satisfy the objectives of the presentinvention, and which would fall within the scope of the presentinvention.

While the foregoing invention has been described with respect to itspreferred embodiments, various alterations and modifications are likelyto occur to those skilled in the art. All such alterations andmodifications are intended to fall within the scope of the appendedclause.

1. A cylindrical roll for use in a heated roll apparatus, said rollcomprising: a surface layer constructed of a material responsive tobeing heated by external magnetic induction, said surface layer coveringthe lateral surface of the roll; an inner layer supporting said surfacelayer, said inner layer being constructed of an insulating materialhaving a thermal mass that is one half or less than the thermal mass ofsteel; a heater for externally heating said surface layer.
 2. Thecylindrical roll of claim 1 wherein said insulating material is aceramic material.
 3. The cylindrical roll of claim 1 wherein saidsurface layer is constructed of a ferrous material.
 4. The cylindricalroll of claim 1 wherein said inner layer has a greater thickness thansaid surface layer.
 5. The cylindrical roll of claim 1 furthercomprising an forced-convection air plenum positioned adjacent said rollto provide inexpensive, external, non-contact cooling of said surfacelayer.
 6. The cylindrical roll of claim 1 wherein said surface layercomprises a plurality of annular sections and said heater comprises aplurality of heaters.
 7. The cylindrical roll of claim 1 wherein saidheater is an induction heater.
 8. A cylindrical roll for use in a heatedroll apparatus, said roll comprising: a surface layer constructed of amaterial responsive to being heated by external magnetic induction, saidsurface layer covering the lateral surface of the cylindrical roll; aninsulating layer supporting said surface layer; an inner layersupporting said insulating layer; a heater for externally heating saidsurface layer.
 9. The cylindrical roll of claim 8 wherein said surfacelayer comprises a plurality of annular sections and said heatercomprises a plurality of heaters.
 10. The cylindrical roll of claim 8wherein said heater is an induction heater.
 11. A cylindrical roll foruse in a heated roll apparatus, said roll comprising: a surface layerconstructed of a material responsive to being heated by externalmagnetic induction, said surface layer covering the lateral surface ofthe cylindrical roll; an aluminum core supporting said surface layer; aheater for externally heating said surface layer.
 12. The cylindricalroll of claim 11 wherein said surface layer comprises a plurality ofannular sections and said heater comprises a plurality of heaters. 13.The cylindrical roll of claim 111 wherein said heater is an inductionheater.
 14. A cylindrical roll for use in a heated roll apparatus, saidroll comprising: a single cylindrical contiguous body of a material thatis responsive to induction heating and has a thermal mass that is onehalf or less than the thermal mass of steel; a heater for externallyheating said surface layer.
 15. The cylindrical roll of claim 14 furthercomprising fluid-carrying chambers within said single cylindricalcontiguous body.
 16. The cylindrical roll of claim 8 wherein saidcontiguous body is made from carbon fiber composite.
 17. A cylindricalroll for use in a heated roll apparatus, said roll comprising: a singlecontiguous cylindrical body constructed from a material responsive toheating by magnetic induction, said single cylindrical contiguous bodyhaving a diameter of less than twelve inches; a magnetic inductionheater for externally heating said surface layer.